In many food processing operations, pieces of vegetable or fruit are fried for the crisp industry and their fat content ratio is too high, resulting in food products that are unhealthy and unappetising.
Further the colour and shape of the raw product after frying has often changed dramatically from the original raw material being used. The sugar content in the vegetable used has the effect that the vegetable, after frying, has a slightly burnt taste and look to it. In order to limit the adverse effect of frying on sugars, raw fruits and vegetables are selected for their low sugar contents and many fruits and vegetables are simply not considered to be suitable for producing a fried, dry snack food, e.g. onions, tomatoes, watermelon, and many more A view is held in at least some circles in the snack food industry that fruit and/or vegetable based snack food products would be more appealing if they could retain more of their original shape, colour and taste.
Expansion of the raw material has also been attempted by many different methods although the result has not yet been favourable thus far, because the extent of expansion is often insufficient and/or the products lose their original shape.
The method currently used most extensively in the snack food industry for manufacturing crisps, involves the raw product having a long exposure to oil in a frying process and the end products having a high fat content averaging 32%-38% (all percentages herein are by mass). These processes are completely unsuitable for high sugar content fruits and vegetables, which burn/caramelise and thus acquire an unpalatable taste and texture, in addition to adverse health effects of burning.
Other methods used in the snack food industry include a process whereby the raw material is sliced and then conveyed through a liquid bath containing agents (such as additives, bleaches and starches) needed to change the material to meet the specification for the final product. The material is then conveyed directly to the fryer. These methods also result in a high fat content in the finished product.
If smaller batch methods of frying are used, the likelihood of contamination increases, because more human contact with the product is required. Batch fryer systems also typically produce products that are darker in appearance and more caramelised, and which has a higher acrylamide content. Acrylamide is considered to pose health risks. Batch processes are also typically commercially less efficient than continuous processes.
The present invention seeks to provide for the manufacture of a crisp snack product that retains the flavour, colour and taste of the raw product to a large extent and that has an acceptably low fat content. The invention further seeks to increase expansion of the raw product, preferably near to the initial size of the raw product, and to retain the expanded shape as far as possible in the end product. The invention seeks to provide these advantages for snack food products manufactured from various ingredients, many of which are not normally suitable for crisp processing, including fruits, vegetables and gelatinizable proteins.
The invention further seeks to conserve energy and to provide for the continuous operation of the vacuum expansion unit, thereby to reduce the human contact with the product and thus reduce the risk of contamination and breakage—preferably with no human contact to the product after slicing of the raw product.
In addition, the invention seeks to provide for snack food manufacturing with low skills requirements